RESEARCH DESIGNS

OVERVIEW

EXPERIMENTAL DESIGNS

When the Research Question Deals “with what happens if”

Experimental Designs-random assignment

• pretest data cannot be collected

• postest only design

• pretest data can be collected

• pretest-postest design

QUASIEXPERIMENTAL DESIGNno random assignment to groups

• pretest data cannot be collected

• postest only design

• pretest data can be collected

• pretest-postest design

Causality

• TEMPORAL SEQUENCE

• CONCOMITANT VARIATION

• ABSENCE OF COMPETING EXPLANATIONS

EXPERIMENTATION

• RANDOMIZATION

• CONTROL

• MANIPULATION

LOGIC OF A TRUE EXPERIMENT

• When one starts a study with two groups who are equal with respect to important variables, administers a treatment to one group (experimental group) and not to the other (control group) holding all other conditions constant, any differences in the dependent variable following treatment probably were the result of that treatment.

Experimental Designs

O=measurement of dep. variable

X=application of indep. variable

R=randomization

Pretest-postest experiment

R O X O

R O O

Solomon Four group

R O X O

R O O

R X O

R O

Postest Only

R X O

R O

Repeated Measures

R OOOO X OOOO

R OOOO OOOO

FACTORIAL DESIGN

experimental if random assignment to cell

Advantages of Experiments

• -test cause and effect

• -control threats to internal validity

Disadvantages of Experiments

• -assumes all of the relevant variables have been identified

• -some variables not manipulable

• -randomization may pose difficulties in field studies

• -Hawthorne effect may not be avoidable

quasiexperimental designs

• lack either randomization and or a control group.

(always have manipulation)

Nonequivalent control group

O X O

O O

Postest only-nonequivalent control group

X O

O

Time Series-non equivalent groups

OOOO X OOOO

OOOO OOOO

Time series design

OOOO X OOOO

Crossover design

OO X OO X OO OO

Advantages of Quasi-Experiments

• -practical, feasible,generalizable

• -adaptable to field studies

• -for some hypotheses they may be the only way to test

• -may save some experiments that suffer from attrition

Disadvantages

• -less confidence in causality

• -need a priori controls

• -must rule out alternative explanations

• -need more replication

EVALUATION RESEARCH

objectives:• --to discover whether and how well

objectives are being fulfilled

• --to discover the reasons for specific successes and failures

• --to direct the cours of experiment with techniques for increasing effectiveness

• --to uncover principles underlying a successful program

• --to redefine goals and objectives and means of obtaining them

Nonexperimental designs

DESCRIPTIVE/EXPLORATORY SURVEY

• collect detailed data on the status quo

• determine differences between varibles

Descriptive/Survey Research

• CHARACTERISTICS

• ATTITUDES

• FACTS

• OPINIONS

• BELIEFS

• BEHAVIORS

Descriptive Surveys

• Use: questionnaires or interviews

• Large samples

• Superficial information emphasizes breadth rather than depth.

• Researcher needs knowledge of techniques.

• Can be costly.

Descriptive Correlational Studies

• Tests covariance between variables

advantages increased flexibility when investigating

complex relationships among variables efficient and effective method of collecting a

large amount of data about a problem potential for practical application in clinical

settings foundation for future experimental research

studies explores relationships between variables that

are inherently not manipulable

Disadvantages:

the researcher is unable to manipulate the variables

generalizability is decreased (preexisting groups)

no causal relationship

EX POST FACTO DESIGNS

“natural experiment”

• independent variable not manipulated

Types of Ex Post Facto Studies

prospective retrospective

longitudinal cross-sectional

advantages:

• similar to correlational advantages

• realistic and natural

disadvantages:

• no causality

• must rule out alternative explanations

• finding similar comparison groups difficult

Methodological Research

• Instrument Construction and Testing

(psychometrics)

• Perfecting Research Techniques

METAANALYSIS-synthesis of research findings